1. Field of the Invention
The present invention relates to a functional device unit, which includes a semiconductor device implemented thereon, and method of producing the unit.
2. Description of the Related Art
Recently, as the MEMS (Micro Electro Mechanical Systems) technology progresses, various functional devices are promoted to combine with others. Ideally, it is preferable to integrate various functional devices, beginning with semiconductor devices, monolithically on an identical substrate. Considering electromagnetic and mechanical characteristics of each functional device, however, the monolithic integration is not applicable in many cases practically. In these cases, a method of hybrid implementation is employed to implement different functional devices in a batch and then combine them.
An example of such the hybrid implementation includes a structure for implementing semiconductor devices such as LSI, light emitting diode (LED), laser diode (LD) and photodiode (PD) in a recess (cavity) formed on a silicon base and the like. This implementation structure can be applied, for example, to a sensor head in an optical encoder.
FIG. 1 shows an example of such the implementation structure for semiconductor devices. A silicon substrate 1 has a recess (cavity) 2 formed thereon, which is employed to implement a semiconductor device 3 therein. The semiconductor device 3 has terminal pads that are connected to terminal pads 4 formed on a surface outside the cavity 2 via bonding wires 5.
The implementation structure shown in FIG. 1 has the following disadvantages. First, if the cavity has a deep step, it raises a difficulty for wire bonding and needs longer wires additionally. Therefore, disturbances such as vibrations easily influence on the structure, thereby reducing its reliability. In addition, a large stray capacitance of the wire effects electrically on the structure to cause performance degradations such as a signal delay.
The present invention has an object to provide a functional device unit capable of having an improved reliability and performance, and method of producing the unit.
A functional device unit, according to the present invention, includes an insulating substrate having a recess formed in a surface thereof; a wiring layer patterned on the surface of the substrate, the wiring layer continuously extending from the bottom of and via the side of the recess to the top surface of the substrate; and a semiconductor device implemented in the recess of the substrate in a flip-chip manner.
According to the present invention, a base for implementing semiconductor devices has a recess formed thereon. Awiring layer is formed on the bottom of the recess and continuously extends therefrom via the side of the recess to the top surface of the substrate. A semiconductor device is mounted on the implementation base in a flip-chip manner. Therefore, the functional device unit obtained is not influenced frommechanical disturbances and has high reliability, differing from those obtained by the conventional method of implementation using the wire bonding. Electrically, it can reduce a signal delay and achieve a high performance.
The functional device according to the present invention may serve, for example, as a sensor head of an optical encoder. In this case, a photodetector chip is implemented as the semiconductor device.
A method of producing a base for implementing a functional device, according to the present invention, has the steps of forming a recess in a surface of an insulating substrate; burying an insulating layer in the recess to planarize the substrate, the insulating layer consisting of a material different from the substrate; forming a photoresist mask over the substrate planarized with the insulating layer buried, the photoresist mask having a groove for wire-burying continuously extending from the top of the insulating layer to the outside of the recess; etching the insulating layer to remove parts exposing through the groove of the photoresistmask; depositing a conductive layer over the resist mask remaining on the substrate to form a wiring layer in the groove, the wiring layer continuously extending from the bottom of and via the side of the recess to the top surface of the substrate; and removing the photoresist mask and the insulating layer successively.
The method of producing according to the present invention employs the step of burying an insulating layer and the step of lifting-off to form the wiring layer on the substrate surface that has a step. That is, deposition of the insulating layer planarizes the recessed surface of the substrate. Then, lithography is employed to formaphotoresistmaskhavinga groove for wire burying on the planarized substrate, and a conductive layer is buried in the groove. Patterning the conductive layer is performed by the lift-off method, which removes the grounding insulating layer and photoresist mask. As a result, even though the recess in the implementation base has a deep step, the wiring layer can be reliably formed across the step.
A method of producing a functional device unit, according to the present invention, has the steps of forming a recess in a surface of an insulating substrate; burying an insulating layer in the recess to planarize the substrate, the insulating layer consisting of a material different from the substrate; forming a photoresist mask over the substrate planarized with the insulating layer buried, the photoresist mask having a groove for wire-burying continuously extending from the top of the insulating layer to the outside of the recess; etching the insulating layer to remove parts exposing trough the groove of the photoresist mask; depositing a conductive layer over the photoresist mask remaining on the substrate to form a wiring layer in the groove, the wiring layer continuously extending from the bottom of and via the side of the recess to the top surface of the substrate; removing the photoresist mask and the insulating layer successively; and implementing at least one semiconductor device in the recess of the substrate in a flip-chip manner.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.